Every detail of this indiscriminate mass murder seemed meticulously planned.

The selection of a hotel room overlooking a music festival, days before the attack. The cache of 23 weapons inside the gunman’s Las Vegas suite. And thousands of rounds of ammunition — plus an ingredient used in explosives — inside the killer’s home and car.

Yet no one knows why Stephen Paddock morphed from a retired accountant to a mass murderer. His relentless gunfire — police say he fired for nine minutes after the first 911 call — on country music fans at an outdoor concert left 59 people dead.

About the cameras, the sheriff said: “I’m not aware of any transmission. But there (were) cameras.” While he didn’t know the specific number, one camera was located on a service cart outside the room, the sheriff said. “I anticipate he was looking for anybody coming to take him into custody.”

Click here or scroll down to the bottom of the page for the news conference livestreamed on the Fox 4 KC Facebook page.

Other points discussed at the news conference:

Police are reviewing body cameras that 67 officers were wearing at the festival and other areas.

There is an internal investigation underway to determine who leaked to the public the pictures of the guns found in the hotel room

They said Paddock’s girlfriend is still in the Philippines and they are working to get her back to Las Vegas.

MGM has donated $3 million to the help fund (See more on that below.) They are still working on how the money will be distributed, but they are hoping it will cover surgeries, travel expenses, etc.

The sheriff confirmed the gunman had cameras set up, including one on a room service cart. The sheriff said he thinks the cameras were used by the gunman so he could see when someone was going to enter his hotel room.

There are still 527 people trying to recover from injuries — everything from gunshot wounds to stampede injuries suffered when 22,000 people tried to flee the gunman’s aim.

So far, police believe Paddock acted alone — which could make the motive harder to determine.

$3.5 million raised

Countless strangers have rallied to support victims, donating blood, money and supplies.

By Tuesday afternoon, a GoFundMe page started by a Clark County commissioner had raised more than $3.5 million.

“Funds will be used to provide relief and financial support to the victims and families of the horrific Las Vegas mass shooting,” county commission chair Steve Sisolak wrote.

Throngs of blood donors lined up for hours to help the wounded.

“This is America — people coming together, helping out.” Hector Salas tweeted. “Likely more than 1000 people waiting in line to donate blood.

— Las Vegas police tentatively will give a public update on the investigation at 5 p.m. (8 p.m. ET) Tuesday.

— Authorities continued processing the scene of the killings, where shoes and bags lay scattered.

— Five handguns, two shotguns and a “plethora” of ammunition were found in Paddock’s Reno, Nevada, property, Sheriff Joseph Lombardo said. Authorities previously found 42 guns in Paddock’s Las Vegas hotel room and at his Mesquite, Nevada, home.

‘Did I do enough to help?’

Brian Claypool is grappling with feelings plaguing many of the survivors — an overwhelming sense of guilt and confusion.

“I’m going through some guilt now. Did I help enough people? Because everybody was screaming and yelling. I didn’t know what to do,” Claypool said, choking back tears.

“Who determines who gets killed in this? That’s what I’m having trouble with.”

The Los Angeles resident said he saw a young woman 15 feet away from him get shot.

“She ended up dying. I happened to be in an area where I didn’t get shot. So I guess I have to go the rest of my life wondering why did some of these people die. Why didn’t I?”

The investigation

Paddock’s violent transformation has mystified everyone — his brother, investigators and the families he victimized.

Police had no prior knowledge of the gunman before the attack.

“I don’t know how it could have been prevented,” Lombardo said.

The massacre has no known link to overseas terrorism or terror groups, a US official with knowledge of the case said.

And authorities say it’s too early to tell whether the massacre was an act of domestic terrorism.

“We have to establish what his motivation was first,” Lombardo said.

For an act to be considered terrorism, it must appear that it was intended to intimidate or coerce a civilian population, or try to influence political change.

The gunman’s brother, Eric Paddock, said he was “completely befuddled” by his brother’s actions.

He said Stephen Paddock was an avid gambler who had “no history of violence. No history of anything — couldn’t give a s*** less about politics, religion, pointy hatted people, etc, etc. He just wanted to get a freaking royal flush.”